The present invention relates to valves and in particular to valves having threaded stems.
Threaded stem valves are used in a variety of environments, in particular being within an air conditioning system. The valves have a threaded stem so that the stem can be rotated by an actuating member to move the valve axially toward and away from a valve seat. Generally, such valves are contained within a valve housing which includes the inlet and outlet ports and with various portions of the assembly being held together, for example by brazing. The threaded valve stem has an exterior threaded portion captured within an internal threaded portion of the valve assembly housing.
In order to provide a bright, shiny finish to the parts, and to inhibit corrosion of the parts, generally a plating material is applied to the parts, for example, nickel plating. Since the parts are held together, for example by brazing, the heating and cooling of the parts during the brazing process causes some discoloration of the metal. Therefore, the plating step occurs after all of the parts have been assembled together.
During the plating process, a plating solution is applied to the valve housing, for example by dipping the valve assembly into the plating solution. Following the plating cycle, the valve assembly is dipped into cold running water three to four times to remove all the plating solution from the interior and exterior of the valve. However, despite the repeated dipping and flushing with water, not infrequently the interior portion of the valve assembly will begin to rust within a matter of a few days following the plating procedure. Such rusting not only inhibits movement of the valve since the rusting generally includes the threaded portion of the valve stem, it introduces contaminants into the stream of material flowing through the valve, such as a refrigerant. Such contaminants may detrimentally affect the operation of the device into which the valve assembly is placed.
Therefore, it would be an advance in the art if a solution were provided to overcome the rusting problem within the valve housing.